What are readiness probes used for in Kubernetes?

Readiness probes are essential in Kubernetes as they help determine if a container is ready to handle requests. When a readiness probe is configured, it periodically checks the state of the container by executing a specified command or URL. If the probe fails, the container is marked as "not ready," and traffic will not be sent to it until the probe indicates that it is ready again. This mechanism ensures that only containers that are fully operational and able to serve traffic will receive requests, thereby enhancing the stability and reliability of applications running in a Kubernetes cluster.

The other options pertain to different functionalities within Kubernetes. Measuring CPU usage is typically managed by resource metrics rather than readiness probes, while automatic restarts of containers are handled by liveness probes or the pod's restart policy. Enforcement of network policies is a separate concern related to controlling traffic between pods and does not involve readiness probes. Thus, readiness probes play a crucial role specifically in managing the availability of containers to serve requests.